1. Field of the Invention
The invention relates to an internal combustion engine and a method of detecting an abnormality of an internal combustion engine.
2. Description of the Related Art
When the amount, of air charged in a cylinder (hereinafter, referred to as “charged air amount”) varies among cylinders, combustion pressure also varies among cylinders. Accordingly, Japanese Patent Application Publication No. JP-A-2004-138036 describes an internal combustion engine in which the combustion pressure in each cylinder is detected, and a variation in the charged air amount among cylinders is detected based on the detected combustion pressure in each cylinder.
However, the combustion pressure varies among the cylinders, not only due to the variation in the charged air amount among the cylinders, but also due to a variation in the fuel injection amount or the injection timing of a fuel injection valve, the ignition timing of a spark plug, or the like among the cylinders. Therefore, the variation in the charged air amount among the cylinders cannot be accurately detected by detecting the variation in the combustion pressure among the cylinders. Thus, even if the charged air amount is controlled when the variation in the combustion pressure among the cylinders is detected, the variation in the charged air amount among the cylinders cannot be necessarily reduced.
Further, the charged air amount cannot be accurately detected by detecting the combustion pressure. Thus, even if the combustion pressure is controlled so that actual combustion pressure matches a value detected when the charged air amount matches a target amount, the actual charged air amount does not necessarily match the target amount.